Laid open Japanese Patent Application Publication Nos. 2001-338818 and 2004-207396 disclose a coil component including an internal drum core (first core) and an external core (second core) adhesively fixed to the drum core. Epoxy resin is used as the adhesive agent. These cores are formed of porous material generally produced by sintering, so that minute pores are formed into which the epoxy resin is impregnated to provide anchoring effect.
Due to the impregnation of the epoxy resin, shortage of amount of the adhesive agent may occur. Further, due to difference of osmotic pressure between the epoxy resin and curing agent contained in the adhesive agent, the curing agent is impregnated first prior to the impregnation of the epoxy resin. In this case, sufficient curing of the adhesive agent is not obtainable. Densification of the surface of the core can restrain impregnation of the adhesive agent into the core. However, anchor effect will be degraded.
If the core is made from a ferrite, wettability of the ferrite against the adhesive agent is insufficient. Therefore, an increased surface area is required for adhesive contact between the drum core and the external core. However, a low profile coil component having a compact configuration is required, which decreases the surface area for adhesion, thereby lowering adhesive strength between the drum core and the external core.